Apparatus for feeding a wire covering to a wire within a heatable forming die



H. BURR 3,512,241

A WIRE WITHIN Mafia-1970 7 A WIRE COVERING To lll 'h APPARATUS FOR FEEDING A HEA'IABLE FORMING DIE Filed March 13, 1968 I H H H l I ll l 1 Harvey B urr BY 10 84404145 ha. 7% M ATTORNEYS United States Patent U.S. Cl. 29202.5 6 Claims ABSTRACT OF THE DISCLOSURE This disclosure relates to apparatus for feeding strips of extensible material to a forming die which wraps the material around a moving wire to form an insulation covering. A tension roll arrangement senses extension of the strip due to temperature and tension and actuates a heater which varies the temperature of the strip to control the rate of feed of the strip to the Wire.

BACKGROUND OF THE INVENTION Prior use of spun-bonded polyethylene and other materials suitable for insulating wires has demonstrated that long thin strips of such materials are extensible and elongate depending on the tension induced therein and the temperature of the material. In particular, it has been found that where dies are heated to sufiicient temperatures to permit wrapping and formation of the insulation covering, variations in the amount of extension and elongation in the strip have caused difficulty in accomplishing proper wrapping of the insulation.

The stretching and elongation of the strip varies with the type of insulation material used and also varies with the width and thickness of the strip fed to the die. Spunbonded polyethylene stretches readily when narrow strips of material are fed to forming dies at high speeds. The use of heated dies in wrapping polyethylene insulation has increased the problem of controlling the rate of feed of the material to the die to compensate for such stretching and elongating of the strip.

SUMMARY OF THE INVENTION It has been found that by measuring and controlling the tension of the strip prior to its entrance into the die that the rate of feed of strip to the strand within the die can be regulated to accomplish proper insulation of the conductor.

Broadly, the present invention comprises a die, heating means for controllably heating the die, feeding means for continuously feeding a wire into the die at a controlled rate, supplying means for supplying continuously at tensioned strip of insulation to the die, tension indicating means for indicating the tension of the strip prior to its entry into the die and control means actuated by the indicating means to control the die heating means.

It is a feature of the invention that elongation and extension of the strip is sensed by measuring the tension in the strip prior to its entrance into the die.

It is also a feature of the invention that a tension sensing means is used to control the die heating means so that when the rate of elongation of the tensioned strip is outside the desired range, the temperature of the die heater is varied to change the strip temperature and rate of strip elongation.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a plan view of the apparatus, FIG. 2 is an elevation view of the apparatus, and FIG. 3 is an enlarged partial elevational view of the tension and strip elongation sensing means.

3,512,241 Patented May 19, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the strand or wire 1 is continuously conveyed through the forming die unit 2 by conventional strand handling reels including guide roll 7 and a strand supply reel (not shown). Die unit 2 has a die entrance 2a into which wire 1 and strip 3 are fed with their longitudinal axes substantially parallel to one another. The shape and configuration of die unit 2 causes the narrow strip 3 to wrap around the wire forming an insulation covering. After the insulation wrapping has been accomplished in the die unit 2, the insulated wire 4 passes out through exit 2b and is carried around guide reel 7 to capstan 8. Guide or idler reel 7 has grooves in it to separate and prevent entanglement of the wire. A second insulated wire or strand, which has preferably been wrapped in a similar manner, may be conveyed together with wire 4 to a twinner or other apparatus (not shown).

Strip 3 is removed from supply roll 10 by operation of upper pinch roll 11 and lower pinch roll 12. Lower pinch roll 12 rotates about shaft 13 and is driven counterclockwise, as viewed in FIG. 2, and upper pinch roll 11 is permitted to rotate in a clockwise direction. Alternatively, upper roll 11 may be driven from shaft 13 in such a manner that it rotates at the same surface speed as roll 12. The pinch rolls perform the function of providing a predetermined and controlled rate of linear feed of the strip at a point after it has been removed from the supply roll 10 and before it enters the die unit. Shaft 13 of lower pinch roll 12 has bevel gear 21 secured to it which is driven by bevel gear 22 which in turn is driven from main drive shaft 24 by belt 23. Capstan 8 is also driven by drive shaft 24 through drive arrangement 25. A variable speed gear unit 9 is positioned between sections of shaft 24 to permit the speed of the insulating strip 3 and the wire speed to be varied with respect to one another depending on wire gauge and other variables.

The speed at which the insulated wire 4 is drawn through the machine is determined by the linear speed of the surface of capstan 8, and the speed of strip 3 as it leaves the pinch rolls is determined by the surface speed of driven roll 12. The surface speed of roll 12 is set to be less than the surface speed of capstan 8 to cause during normal operating conditions a desired amount of tensioning and elongation of the strip. The amount of elongation is determined by the relationship between the two surface speeds. This relationship is determined by the setting of the variable speed gear 9 and any desired percentage of elongation of the-strip can thus be obtained by adjustment of the variable speed gear 9. However, the amount of elongation which the strip can tolerate without fracture is determined principally by the temperature to which it has been brought by the heated die 2. If the temperature is too low, the tension in the strip between the pinch rolls and the die will increase and the strip will break before the desired amount of elongation as set by the variable speed gear 9 has been reached. If the temperature is too high, the tension in the strip will reduce and the elongation will be higher than desired. This will cause the pinch rolls to feed a greater length of strip than the length being drawn through by the capstan 8, and the strip will then accumulate in an uncontrolled manner between the pinch rolls and the die.

Strip 3 passes from the pinch rolls over idler roll 15, under tension roll 16 and over second idler roll 17 where it is fed through entrance 2a. of forming die unit 2. Forming die unit 2 causes the strip 3 which is positioned just below wire 1 to be wrapped around the wire to form an insulation covering around the. wire. Preferably a longitudinal wrapping die, as disclosed in my US. Pat. No.

3 3,337,386 issued Aug. 22, 1967, is used to perform the strip wrapping function.

Die unit 2 is heated by an electrical heater 18 which is controlled by control unit 19 which includes a switch for turning the heater on and off and includes a rheostat 20 for varying the electrical current to the heater 18. Die unit 2 is made of metal or other heat conductive material thus permitting heat to flow through from heater 18 to the strip. The strip is preferably a spunbonded polyethylene inulation material, a polypropylene material or other plastic material. Such materials provide satisfactory insulation characteristics and a narrow strip of such materials is controllably extensible when heated and tensioned. For example, a strip of polyethylene material only 7 wide and 1.5 thousandths inch thick is used to wrap a No. 26 A.W.G. wire. The die is heated is facilitate formation of the strip wrapping and its formation as an insulation covering. Heat permits some material to bind to itself after it has been wrapped around the wire thereby forming an insulation covering that resists winding or fraying.

The tension in the strip 3 between pinch rolls 11, 12 and guide or idler reel 7 is caused to vary by reason of variations in elongation and extension of the strip depending on the surface speeds of the pinch rolls and the capstan and depending on the temperature of the strip. It is desired that the rate of feed of the strip to the position where it wraps around the wire be controlled to provide proper wrapping of the insulation in the die. Since variation in elongation of the strip varies the feed rate, the temperature of die is automatically controlled to maintain strip elongation within a desired range. The tension in the strip is measured, indicated and controlled by tension roll 16 and control unit 19 which turns the electric heater on and off in response to signals produced by the tension roll movement. Control unit 19 also has a rheostat 20 which may be manually operated to vary the amount of heat transferred to the strip when the heater is turned on.

Tension roll 16 rotates freely about tension roll shaft 26; however, if desired, the roll 16 and shaft 26 may be fixed together permitting the roll to slide on the moving strip. The ends of shaft 26 are positioned in vertical guide slots 27 of front and back stands 28 and 29, respectively. Tension roll 16 is lowered when tension decreases and is raised when tension increases.

Turning to FIG. 3, tensioning roll 16 is shown positioned for rotation about shaft 26 which shaft has its front end portion in guide slot 27 of front verticallypositioned stand 28. The position of the the apparatus in FIG. 3 illustrates the condition in which heater 18 is turned on and is heating the strip 3. A weight 30 is positioned on pivot-able arm 31 to tension strip 3 in such a manner as to hold the tension roll 16 in approximately the position shown. Weight 30 is slidable positioned to accommodate for variations in the width, cross-sectional area and tensile strength of the strip being handled. Arm 31 is pivoted about axis 32 with one of its ends having a bearing 34 freely rotatable about the front end of shaft 26. Weight 30 is slidable along a portion of arm 31 and has screw 35 to seize it to the arm at selected positions.

As the strip 3 is heated it will increase its rate of elongation thus reducing tension in the strip and permitting roll 16 to move downwardly causing arm 31 to rotate counterclockwise until the arm cont-acts and pushes spring-loaded element 36 of switch 37. Switch 37 is in turn actuated to deenergize heater 18 as element 36 moves upwardly against a spring (not shown). As strip 3 cools and reduces its rate of elongation roll 16' will move upward permitting element 36 to be returned by the spring to a lower position whereby switch 37 will, turn the heater on again. Switch 37 may be of conventional construction to accomplish opening and closing of an electric circuit when element 36 is urged upward or permitted to return to the position shown in FIG. 3. Heater 18 is turned on and oil in response to roll 16 movement as described to maintain a constant tension in strip 3 as it is fed to die 2. Roll 16 moves up and down or remains steady to indicate the amount of tension in strip 3.

In the operation of the invention, it has been found that spunbonded polyethylene has little strength where a die temperature of about 250 F. is maintained for a substantial length of time. A strip temperature range of F. to 200 F. was found satisfactory for spunbonded polyethylene but since the material is a poor conductor of heat a higher die temperature is required to start up within a reasonable length of time. As strip temperatures increases, tension is decreased and the heater is turned off by the control unit. An operator may adjust the position of the weight and the rheostat of the control unit when different strips are being handled or where such adjustments are desirable during a particular run.

Iclaim:

1. An apparatus for controlling the rate of movement of a strip of extensible material within a forming die as the strip is formed around a continuously moving wire comprising (a) conveying means for conveying the wire to be insulated to the die and for conveying the insulated wire from the die,

(b)' supply means for continuously supplying the extensible strip to the die,

(c) heating means capable of selectedly supplying heat to the die for heating the strip to cause it to extend in length,

(d) strip extension indicating means positioned between the supply means and the die for indicating extension of the strip prior to its entry into the die, and

(e) control means operably connected to the extension indicating means to control the heating means,

whereby heat is selectedly supplied to the die as the extension of the strip varies.

2. The apparatus of claim 1 in which the conveying means conveys the wire at a predetermined rate and in which the strip supply means includes strip feeding means for controlling the rate of feed of the strip prior to the entry of the strip into the die.

3. The apparatus of claim 1 having variable drive means for driving both the conveying means and the strip feeding means to coordinate the feed rates of the wire and the strip such that the linear speed of wire conveyed by the conveying means is greater than the linear speed of the strip prior to the entry of the strip into the die.

4. An apparatus for controlling the feeding of a strip of a readily elongated insulation material to a forming die having an entrance and an exit comprising (a) cpnveying means for conveying under tension a conductive Wire into the forming die entrance,

(b) supply means for supplying the strip into said entrance with its longitudinal axis substantially parallel to the longitudinal axis of the wire,

(c) electrical heating means for heating the die and the contained wire and strip,

(d) tension indicating means positioned remotely from the die to indicate tension in the strip as it travels toward the die, said tension indicating means in turn comprising (i) two guide rolls for supporting the strip as it travels toward the die,

(ii) a tension member positioned between said guide rolls and supported by the moving strip such that the member moves as the tension in the strip varies,

(iii) a pivotable member connected to the tension member and pivotable by the tension member when the tension member moves in response to tension in the insulation material; and (e) control means connected to the tension indicating means for controlling the electrical heating means, the control means in turn comprising (i) a switch actuated by the pivotable member,

and (ii) electrical circuit means for energizing the electrical heater when the switch is activated. 5. The apparatus of claim 4 in which the strip supply means includes a pair of pinch rolls which regulate the rate of movement of the strip at a point remote from the entrance of the die,

References Cited UNITED STATES PATENTS 8/1967 Burr 29-2025 3/1968 Petersen 156385 10 THOMAS H. EAGER, Primary Examiner US. 01. X.R. 

